1. Field of the Invention
The present invention relates to a transmitting apparatus, a transmitting method, a receiving apparatus, a receiving method, and a transmitting and receiving system that allow data transmitted from a transmission side to be quickly reproduced from the beginning of the data on a reception side.
2. Description of the Related Art
In a CATV, a so-called NOD (Near On Demand) system of which a content for example data of a movies requested by a user is transmitted from the beginning thereof has been used. The NOD system is generally categorized as a single channel system shown in FIG. 1 and a multiple channel system shown in FIG. 2.
In an example of the single channel system shown in FIG. 1, a content of one second is repeatedly transmitted from the transmission side. At that point, when the reception side waits for a maximum of one second, the reception side can reproduce the content from the beginning. In other words, in the single channel system, the maximum waiting time of a user who has a receiver is one second. When the user waits for one second, he or she can see and/or listen to the content from the beginning. However, in the single channel system, when the length of a content is 10 seconds, the maximum waiting time for the user becomes 10. Likewise, when the length of a content is 30 seconds, the maximum waiting time for the user becomes 30 seconds.
On the other hand, in an example of the multiple channel system shown in FIG. 2, five channels are provided for repeatedly transmitting a content of 31 seconds from the transmission side. In the multiple channel system, the beginning of a content transmitted on one channel is different from that on the immediately adjacent channel by 6.2 seconds (31 seconds/5 channels=6.2 seconds). In other words, when the number of channels is denoted by n and the length of a content is denoted by L, the maximum waiting time becomes L/n seconds. In this case, on the reception side, a content is reproduced from the beginning with a maximum waiting time of 6.2 seconds. In other words, in the multiple channel system, a user who has a receiver can see and/or listen to a content from the beginning with a maximum waiting time of up to 6.2 seconds.
Originally, the technology of the NOD system was designed so that a content for example data of a movie whose broadcast time is around one to two hours is repeatedly transmitted using a plurality of channels and the reception side can see a requested movie from the beginning with a maximum waiting time of 15 minutes on a selected channel. The NOD system has benefits of which a one-way communication line can be used and a complicated control is not required on the transmission side.
In addition, another technology of which the number of channels is increased to more than several tens and the total length of each content is shortened to several minutes is also known. According to this technology, the user can see and/or listen to a content from the beginning with a waiting time of several seconds.
In both the single channel system and the multiple channel system, the maximum waiting time for any portion of a content is constant. For example, when a content of 60 seconds is transmitted with 60 channels, any portion of the content (including the beginning thereof) can be accessed with a maximum waiting time of one second. In other words, in both the single channel system and the multiple channel system, a content is accessed at equal speed.
However, in both the single channel system and the multiple channel system, there is the following relation of proportional:(waiting time)×(number of channels)=(total length of content)Thus, when the maximum waiting time of the same content is shortened, the number of channels (capacity of transmission line) is proportionally increased. Alternatively, assuming that the total length of a content is increased and that the maximum waiting time is not changed, the number of channels should be proportionally increased.